Means for indexing the electron beam in magnetron type beam switching tubes



June 11, 1957 v s. KUCHINSKY 2,795,732

I MEANS FOR INDEXING THE ELECTRON BEAM IN MAGNETRON PE BEAM SW TUBES Filed Jan. 22, 1954 TY ITCHING 5 Sheets-Sheet 1 INVENTO R SAUL KUCHINSKY BY zww June 11, 1957 s, KUCHINSKY 2,795,732

MEANS FOR INDEXING THE ELECTRON BEAM IN MAGNETRON TYPE BEAM SWITCHING TUBES Filed Jan. 22, 1954 5 heetshe 2 m E TARGET 2 v I SWITCHING GRID VOLTAGE Flg. 6

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so 44 so INVENTOR SAUL- KUCHINSKY 5gp. a

June 11, 1957 s. KUCHINSKY 2,795,732

THE E TRON BEAM IN MAGNETRON TYPE BEAM SWI HING TUBES Filed Jan. 22, 195-4 3 Sheets-Sheet 3 MEANS FOR INDEXING F a & J fi & r Ci-u g IIIIIIIIIIII II m INVE NTOR SAUL KUCHINSKY. BY

MEANS FOR INDEXING THE ELECTRON BEAM IN MAGNETRON TYPE BEAM SWlTCI-HNG TUBES Saul Kuchinslry, Phoenixville, Pan, assignor to Burroughs Corporation, Detroit, Mich, a corporation of Michigan Application January 22, 1954, Serial No. 405,589

23 Claims. (Cl. 315-21) This invention relates to magnetron type multiple position beam switching tubes and particularly to means for and a method for pre-setting or indexing the electron beam in such tubes to a predetermined beam position.

Magnetron type multiple position beam switching tubes make use of crossed electrostatic and magnetic fields in their operation. Usually the magnetic field is provided by a hollow cylindrical magnet whose flux permeates the tube in lines which are substantially parallel to the elongated cathode in the spade-cathode region of the tube. Tubes of this general type are disclosed and claimed in the copending U. S. application of Fan and Kuchinsky, Serial No. 370,086, entitled Multi-Position Beam Tube, filed July 24, 1953, now Patent No. 2,721,955. Such tubes have three arrays of electrodes surrounding the elongated thermionic cathode. A cylindrical array of symmetrically disposed beam forming and directing electrodes, known as spade electrodes, surrounds the cathode and is concentric With respect to it. Each spade electrode is insulated from the other space electrodes and is usually connected to a source of potential which is positive with respect to the cathode through a spade impedance which usually is a resistor. The spade electrodes are usually coextensive in length with the electron emissive portion of the cathode and have a curved, usually U-shaped, transverse cross-sectional configuration. The open part of the spade faces outwardly with respect to the cathode.

An array of symmetrically disposed electron receiving or target electrodes surrounds the spades and constitutes the outer array of electrodes of the tube. The target electrodes are equal in number to the spade electrodes and each target is aligned with the space between two adjacent spades whereby electrons which pass through the space may impinge on the target electrode which is associated therewith. Like the spades, each target electrode is connected to a source of potential which is positive with respect to the cathode through an impedance member which is usually a resistor. The output signal from each target electrode is developed across its target impedance member.

The third array of electrodes comprises a plurality of rod-like beam switching electrodes which are equal in numher to the number of spades. Normally, each of the switching electrodes is disposed between an edge of a spade and the target associated with the next adjacent spade. The beam switching electrodes are normally maintained at a positive potential, but this potential is reduced when the switching electrode (or electrodes) are to perform their beam switching function.

When all of the spades are at the potential of the spade power supply, the relationship between the electrostatic and magnetic fields is such that electrons emitted from the cathode follow curved paths around the cathode and substantially no electrons impinge on the spades or other outer electrodes of the tube. If, however, the potential on one of the spades is lowered to, or near to, the potential of the cathode, the configuration of the electrostatic 2,795,732 Patented June 11, 1957 field is changed, especially in the vicinity of the spade having the lowered potential, and a stream or beam of electrons is formed between the cathode and the leading edge of that spade. The edge of the spade to which the beam is attracted is determined by the direction of rotation of the electron beam within the tube (which is determined by the polarity of the magnetic field which permeates the tube). The electron beam locks in at the edge of the spade which is furthest in the direction of the rotation of the beam, and this edge is called the leading edge. The opposite edge of the spade is the lagging edge. The electrons impinging on the edge of the spade cause electron fiow through the spade impedance and, if the spade resistor value is properly chosen, the electron flow therethrough reduces the potential of the spade sufliciently to maintain the beam locked in even though the external means for reducing the potential of the spade be removed. However, it the switching electrode or grid at the next adjacent spade has its potential reduced, the electron beam which is locked on the lagging spade (and which also impinges on the target electrode associated with that spade) changes its shape. If the reduction in potential on the switching electrode is sufiicient, the beam will spread to the extent that part of the electrons of the beam spread and impinge on the leading spade with which the switching electrode is associated, causing a'voltage drop on that spade. Because of the tendency of the electron beam to be rotated by the magnetic field as previously mention, the beam then switches to the spade having the lowered potential which is furthest in the direction of rotation of the beam.

Such tubes find considerable use as counters and other beam switching or control devices, and often two or more of the tubes are operated in cascade. The problem arises as to how the beam might be preset or indexed at any predetermined spade or beam position; Manually momentarily shutting off all power to the tube in order to clear the tube and then grounding the desired spade, for example, to re-form the electron beam at the predetermined beam position, is possible. While this method of indexing the beam works in a satisfactory manner, it is not a method which is adaptable to high speed electronic control of the tube. Electronic means for indexing the tube by first clearing the tube and then pulsing a spade down to re-torm the beam are likewise known, but such systems require control pulses of the order of 50 volts or even more, depending on circuit parameters. It should be noted that in the prior art indexing means it is necessary to extinguish the electron beam prior to indexing since the beam, when locked in at one position, can not see ahead" to all other beam positions in the tube. Extinguishing the beam requires the expenditure of power and usually involves another tube in the cathode circuit of the tube. Further, turning the beam on and off during the beam indexing operation may shorten the life of the cathode of the beam switching tube.

A principal object of the present invention is to provide an improved method of and means for controlling the electron beam in a magnetron type multiple position beam switching tube.

Another object of the present invention is to provide improved, faster acting means for controlling the electron beam in a multiple position beam switching tube.

A further object of the present invention is to provide improved means for indexing the electron beam of a magnetron type multiple position beam switching tube which is operable by control impulses which are available in the equipment with which the tube is to be used.

An additional object of the present invention is to provide an improved, more economical means of indexing the electron beam in a magnetron type multiple position beam switching tube.

Yet another object of the present invention is to provide a method of and means for indexing the electron beam to any predetermined beam position without cutting off the electron beam.

A still further object of the present invention is to provide an improved, more reliable method of and means for indexing the electron beam of a magnetron type beam switching tube which requires no power from the indexing control pulse source.

In accordance with one embodiment of the present invention the electron beam in a magnetron type multiple position beam switching tube is indexed or pre-set to a specified beam position by causing the electron beam within the tube to oscillate or advance in a self-controlled manner from one beam position to another until it reaches the beam position to which it is to be indexed. The beam switching electrode or grid associated with the index beam position is biased to prevent advancement of the beam beyond the index beam position during the time the oscillating condition is present in the tube.

The invention, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

Fig. 1 is a sectional view of a magnetron type multiple position beam switching tube and a schematic diagram of a beam advancing and indexing circuit associated with the tube in accordance with the present invention;

Fig. 2 is similar to Fig. 1 except that the circuit provides for push-pull input pulsing to advance the beam;

Fig. 3 is similar to Fig. 1, but the circuit has a provision for reducing the spade-cathode voltage to cause the tube to oscillate;

Fig. 4 is similar to Fig. l, but the circuit has a provision whereby a single pulse applied to any switching grid is utilized to cause the tube to oscillate and then-to index the electron beam at the beam position associated with the grid to which the pulse is applied;

Fig.5 is a sectional view of a magnetron type switching tube and a schematic diagram of a beam advancing and indexing circuit in which a set of auxiliary switching grids are utilized to cause the tube to oscillate. prior to the indexing or pre-setting of the electron beam;

Fig. 6 shows the relationship between the spade voltages, switching grid voltages, :and target voltages which provide stable operation of the switching tubes illustrated in connection with the previous figures. A constant magnetic field around the tube is assumed; and

Fig. 7 is a perspective view of a magnetron type beam switching tube suitable for use with the present invention.

Referring to Figures 1 and 7, there is shown a tube 20 having an envelope 22, a centrally disposed elongated rod-like thermionic cathode 24 which is surrounded by an array of elongated spade electrodes 26 which have a somewhat U-shaped cross sectional configuration. An array of elongated target electrodes 28 having an L-shaped cross-sectional configuration surrounds the array of spade electrodes 26. The target electrodes 28 are equal in number to the spade electrodes 26, and each target electrode 28 is disposed in alignment with the space between two adjacent spades. An array of rod-like switching grid electrodes 30 is disposed between the array of spade electrodes 26 and the array of target electrodes 28, each of the switching grids being generally aligned with respect to an edge of a spade electrode.

Leads to the cathode 24, spades 26, targets 28 and switching grids 30 are brought out through the tube envelope 22 to base pins 32.

In the embodiment of the present invention which is shown in Fig. 1 each of the spades 26 is connected to a source of positive potential, such as the battery 34, through the individual spade impedance resistors 36. The spade resistors 36 may, if desired, be included within the tube envelope. Arranging the spade resistors 36 within the envelope results in a reduction of the stray capacitance of the tube and furthermore permits a reduction in the number of leads to be brought out to the base pins of the tube. Tubes which are designed for operation at high beam switching rates often have internal spade or target resistors, or both. The ohmic value of each of the spade resistors 36 is usually substantially the same, and is high enough that the voltage drop due to beam current passing therethrough reduces the potential on the spade on which the beam impinges to, or near to, the potential of the cathode 24. Each target electrode 28 is connected to a source of positive potential, illustrated as the battery 38, through individual target impedances 40 which are illustrated as being resistors. The output signal from each beam position is developed across its target resistor and is taken from the output terminals 56. The spade impedances may include elemen-ts other than resistors, but always include a resistance element which provides the direct current voltage drop across the impedance which is required to maintain the spade at a lower potential and to lock in the electron beam at a particular spade.

Each of the switching elements or grids 30 is connected to a common lead 42 through an individual switching grid resistor 44. The common lead 42 is connected through a series resistor 46 to a source of positive potential 48 which is illustrated as being a battery.

Advancement of the electron beam from one beam position to another adjacent beam position is accomplished by applying a negative pulse to the input terminal 50 which is conductively connected to the common lead 42. A beam position in the tube comprises a spade upon which the electron beam may lock in and includes the electrodes adjacent to the lock in spade which influences the beam.

The duration of the negative pulse which is applied to the input terminal 50 controls the number of beam positions through which the electron beam will advance. If the beam is to be advanced one position at a time, the pulse duration may, for example, be .1 microsecond or less, depending on the beam transfer time from one beam position to the next adjacent beam position.

In many tubes it is desirable to bias the switching grid 30 to a positive potential as indicated by the battery 48. While the actual switching grid pulse voltage required to reliably switch the electron beam may vary because of tube, magnetic field, or circuit considerations, pulses of 20 volts negative amplitude are average, but switching with smaller pulses is possible and has been successfully accomplished. A negative pulse of 20 volts amplitude, for example, applied to the switching grids 30 would cause the electron beam 52 to fan out from the spade 26 upon which the electron beam is locked in. As a result of the fanning out of the electron beam adjacent to the edge of the spade 26 on which the beam is locked in, part of the beam impinges on the next adjacent or leading spade which lies in the direction of the rotation of the beam. When part of the electron beam 52 impinges on the leading spade the potential of that spade is dropped to, or near to the potential of the oathode due to the beam current producing a potential drop across the spade load resistor and the electron beam then transfers (or switches) and locks in on the leading spade. Since the time required for the beam to switch from one beam position to another may vary in accordance with tube geometry and circuit parameters, the duration of the 20 volts negative switching pulse must be controlled accordingly. Negative pulses of longer duration result in the beam switching more than one beam position. The above described arrangement concerns beam advancement generally, but it is often desirable to reset the beam at a pre-determined position, such as a zero beam position for example.

In order to reset the electron beam at a desired beam position in accordance with the present invention a negative input pulse of 20 volts or more amplitude is applied seams to the input terminal 50, thus causing the beam to advanc'e. Since it may be desired to preset the beam at any one of the beam positions in the tube, the duration of the negative pulse applied to the input terminal 50 must be at least equal to the time required to switch the beam from one beam position to the next adjacent beam position multiplied by the number of beam positions in the tube. Simultaneous with or during the application of the negative pulse which causes the beam to switch in an oscillatory or self-controlled manner, a positive pulse which is equal to or greater in magnitude than the negative pulse is applied to the terminal 54 of the particular switching grid 30 of the beam position the electron beam is to be preset or indexed. Thus, all of the switching grids except the one to which the positive pulse is applied are maintained at a sufficiently reduced potential to cause the electron beam to switch as previously described in connection with the normal advancing of the beam from spade to spade in response to input pulses. Because of the longer duration of the negative input pulse used in presetting the beam, the electron beam 52 advances o1 oscillates around the tube from spade to spade (or from beam position to beam position to be more technically accurate) until it is prevented from advancing further by the positive pulse which is applied to the switching grid at the index beam position. The negative pulse which causes the electron beam to oscillate within the tube produces a voltage drop across the series resistor 46, thereby reducing the potential on all the beam switching grids. However, since each of the beam switching grids is connected to the lead 42 through an individual switching grid resistor 44, the application of a positive pulse to any of the input terminals 54 would tend to maintain the beam switching grid 30 to which the positive pulse was applied at a positive potential because of the voltage drop across its switching grid resistor 44. The positive pulse applied to the input terminal 54 also results in the raising of the potential across the series resistor 46 since the resistor 46 is connected in series with each of the switching grid resistors 44 and through the battery 48 to ground. The voltage drop across the series resistor 46 resulting from the application of a positive pulse to one of the input terminals 54 thus tends to raise the potential on each of the beam switching grids 30. The relationship between the ohmic value of the beam switching grid resistors 44 and the resistor 46 and the relative magnitude of the negative and positive pulses applied to the switching grids 30 must be such that the application of the positive pulse to the input terminal 54 does not cause the electron beam 52 to cease its oscillatory advancement prior to the time the beam advances to the beam position associated with the switching grid at which the positive pulse is applied through the input terminal 54. Thus, by means of pulses of relatively small amplitude, in the neighborhood of volts, for example, and without cutting off the electron beam within the beam switching tube, the electron beam may be rapidly and accurately indexed at any chosen beam position. For many tubes the time required to index the beam will not be greater than 1 microsecond.

The arrangement shown in Fig. 2 is similar to that shown in Fig. l. The spade electrodes 26 and the target electrodes 28 and their respective impedance elements are connected in the same manner as described with respect to the arrangement shown in Fig. 2. Each of the switching grids 30 is connected to a common lead through a switching grid resistor 44 as in Fig. 2, but in the switching grid arrangement of Fig. 2 two common leads, 58 and 60, are provided. Alternate one of the switching grids 30 are connected to the common lead 58 and the remainder of the switching grids are connected to the common lead 60. A resistance element 62 is connected to the common lead 58 and a similar resistance element 64 is connected to the common lead 60. The ends of the resistor 62 and resistor 64 which are remote from the common leads 58 and 60 are conductively connected to each other and thence to a source of positive potential 48 through a resistor 66. An input terminal 68 is provided at the junction between the resistor 66 and the end of resistors 58 and 60 which are joined together. An input terminal is conductively connected between the resistor 62 and the common lead 58. An input terminal '72 is conductively connected between the resistor 64 and the common lead 60. An input terminal 54 is conductively connected between each of the switching grid resistors 44 and the switching grid 30, as in Fig. 1.

The normal switching of the electron beam using the circuit of Fig. 2 is diiferent than described in connection with Fig. 1 because alternate switching grid electrodes are connected to each of the common leads 58, 60. A negative beam switching pulse applied to input terminal 70 or 72 will therefore advance the electron beam only a single position, since the next adjacent switching grid in each case will remain positive in potential. With this arrangement the duration of the negative switching pulse used to switch the beam need not be accurately controlled. In fact, direct current may be used to switch the beam from one position to another.

Still referring to Fig. 2, when it is desired to index the tube to a specified beam position, a negative pulse is applied to the input terminal 68 in order to lower the potential of all of the switching grids 30 and cause the beam to oscillate around the tube as previously described in connection with Fig. l. A positive pulse is applied to the input terminal 54 of the switching grid 30 which is to be used to determine the beam position to which the electron beam of the tube will be indexed. Because the positive pulse applied to any of the input terminals 54 will produce a voltage drop across one of the switching grid resistors 44, either across resistor 62 or 64, and across the resistor 66, the ohmic values of these resistors and the magnitudes of the positive and negative pulses applied to terminals 54 and 68 must have such a relationship that the positive pulse applied to the input terminal 54 does not produce sufficient voltage drop across the other resistors to cause the tube to cease oscillating before the electron beam 52 advances to the index beam position.

The indexing circuit arrangement shown in Fig. 3 is similar in one respect to the indexing arrangement of Fig. l in that a negative pulse which is applied to the terminal 50 is used for normal step-by-step advancing of the electron beam within the tube. The electron beam is caused to oscillate within the tube during the indexing operation, however, by applying a positive pulse across the resistor 74 which is connected between the cathode 24 of the beam switching tube 30 and ground, reducing the spadecathocle potential difference. If the reduction in the spadecathode potential exceeds a critical value with respect to the switching grid potential the electron beam oscillates within the tube just as described in connection with Figs. 1 and 2 where the oscillatory beam advance occurred as a result of a negative pulse applied to the switching grids 30. The reason why the beam oscillates within the tube when the spade-cathode potential is reduced may be more readily explained with reference to Fig. 6.

The solid sloping lines 76a, 76b in the graph represent target potentials of a beam switching tube. The spadecathode potential is represented by the ordinate and the switching grid potential by the abscissa of the graph. In the graph of Fig. 6 the switching grid potential is in the negative polarity with progressively negative values being presented to the right along the abscissa. The solid lines X, Y show that for a particular spade-cathode voltage C the switching grid voltage must be equal to or greater than Y in order to provide stable electron beam control in the tube for a given spade voltage 76A. The dotted lines X1, Y1 shows that if the spade-cathode voltage is reduced, the switching grid potential must be increased to provide stable electron beam control. Conversely, increasing the spade-cathode voltage as shown by the lines X2, Y2 results in less switching grid voltage "7 being required. Thus, it can be seen that, for a given target potential, as the spade-cathode voltage increases, less switching grid potential is necessary to prevent oscillation of the electron beam. Conversely, if the spade cathode voltage is reduced, the switching grid bias voltage must be increased to prevent oscillation of the beam. In the case of the indexing arrangement shown in Figs. 1 and 2, the beam is caused to oscillate to the indexing position by reducing the potential on all. the switching grids, except the indexing grid, to below the critical value. Thus, the electron beam is caused to momentarily oscillate until the beam is indexed.

In Figs. 3 and 4, the spade-cathode potential is momentarily reduced below the critical value with respect to the switching grid voltage and the electron beam in the tube oscillates until it reaches the indexing switching grid 30 which is biased to a potential which is higher than the critical switching grid voltage.

In the above statements it is assumed that target potentia ls and magnetic field strength are held constant. Changing of the potential on all the targets, however, may also be used to cause the electron beam to oscillate. This possibility is shown by the parallel relationship between the lines 76a and 76b in Fig. 6. The same result can be achieved by varying the strength of the magnetic field, although this means of producing oscillation of the electron beam is usually inconvenient as compared to changing of potentials on the other tube electrodes.

Returning now to Fig. 3, the positive pulse applied to the terminal 78 across the resistor 74 reduces the spadecathode voltage below the critical value with respect to the fixed switching grid voltage, thus causing the electron beam to oscillate within the tube. A positive pulse, however, is applied through the input terminal 54 of the switching grid 30 at the beam position where the beam is to be indexed to raise the switching grid potential above the critical value for the existing spade-cathode potential and thus stop the electron beam at that position. The positive pulse applied to the switching grid must last as long as the positive pulse applied across the resistor 74, or longer, or the electron beam would continue to oscillate until the pulse applied across the resistor 74 ended. For the purpose of illustration, each of the switching grids 30 are connected through a resistor 44 to a single common lead 42 as in Fig. l. The pushpullv switching grid arrangement shown in Fig. 2 or other suitable arrangements, could be used.

The arrangement shown in Fig. 4 is generally similar to the arrangement of Fig. 3. However, additional circuitry is added in order to provide for the oscillatory advancement of the electron beam 52 within the tube and the indexing of the beam at a specified beam position by the application of a single input pulse of positive polarity. Normal .step-by-step advancement of the beam is accomplished, as in Fig. 3, by the application of a negative pulse of the required duration to the input terminal 50. In order to preset or index the electron beam, a positive pulse may be applied to any one of the input terminals 54 which are conductively connected between each of the switching grids 30 and the switching grid resistors 44.

In Fig. 4 a diode 80, which may be either a crystal diode or an electron tube diode, is connected in a suitably polarized manner between each of the switching grid input terminals 54 and the junction between the cathode resistor 82 and cathode 84 of the vacuum tube 86 via the common lead 88. The control grid 90 of the tube 86 is grounded or otherwise biased when the anode 92 of the tube 86 is connected to the cathode 24 of the beam switching tube 20. The application of a positive pulse to an input terminal 54 raises the potential of the switching grid 30 associated with that input terminal and at the same time, due to conduction through the diode 80, causes'the cathode 84 of the tube 86 to become positively charged 'with respect to the grid 90. Increasing the bias on the tube 86 increases the voltage drop across the cathode tube 86, which, in turn, causes the potential on the cathode 24 to rise. The change in bias on the tube 86 results in an increase in the resistance across the tube. Thus, when it is considered that the beam switching tube '20 and the tube 86 are connected in series across the spade power supply, an increase in the resistance represented by the tube 86 results in an increased portion of the power supply potential appearing across that tube.

The result is that the spade-cathode potential of the beam switching tube 20 is decreased below the critical point with respect to the positive potential on the switching grid. This decrease in spade-cathode potential causes the electron beam to oscillate within the tube until the electron beam reaches the beam position associated with the switching grid 30 to which the positive pulse has been applied. The electron beam cannot advance further because the potential on this switching grid is more than the critical potential which is required to produce stable beam switching operation of the tube at that beam position, and the beam locks in and indexes at that position. The duration of the positive pulse applied to the switching grid 30 must be of suflicient duration to allow the electron beam to oscillate and to advance one complete revolution of a tube if positive indexing is to be achieved. Because the increase in positive grid potential necessary to secure stable operation of the tube may be small (5 volts for example) and because a small voltage is all that is required to change the bias of the tube 84 and thus cause the beam switching tube 20 to oscillate, the arrangement of Fig. 5 provides a simple means for indexing the electron beam in the beam switching tube. The tube 26a illustrated in Fig. 5 is similar to the tube 20 shown in Fig. 7, but has a second set of switching gn'ds 94. One of the switching grids 94 is disposed generally between the leading edge of each spade 26 (the edge of the spadeon which the beam locks in) and the target electrode 28. (Each of the switching grids 30, of the first set, is disposed between the lagging edge of a spade 26 and a target electrode 28.) It has been found that the switching grids 94 of the second set may also be used for beam switching purposes by biasing them to near to a critical negative value and then applying a further switching pulse of negative polarity to cause the beam to switch to the next adjacent position. This property is utilized in the electron beam indexing circuit of Fig. 5.

Normal beam advancement is achieved by applying negative pulses to the terminal 50 and across the resistor 46, as was done in Fig. 1, for example.

The electron beam 52 is caused to oscillate and advance by the application of negative pulses to the terminal 96. Each of the switching grids 94 is connected to a common lead 98 which is connected through a resistor to a bias source 102, indicated as a battery. The terminal 96 is connected between the lead 98 and the resistor.100. Thus, the negative pulse applied through the terminal 96 and across the resistor 1G0 biases the switching grids 94 beyond the critical point and the electron beam oscillates. A positive pulse is applied to the terminal 54 associated with the beam position to which the beam is to be indexed, thus acting as an anti-switching grid and preventing the further advancement of the electron beam 52. As in the previous indexing arrangements, the beam oscillation producing pulse must have a duration equal to the time required for the electron beam to make at least one complete revolution in the tube 20a. Likewise the positive pulse applied to the switching grid 30 at the beam indexing position must be applied while the electron beam 52 is oscillating and must continue at least as long as the negative pulse is applied to the switching grids 94.

While the'present invention has been described in connection with beamswitching tubes having switching grids, the invention .is by no means limited to use with such tubes. :Individual .output or target electrodes may be electron beam beyond said predetermined beam position, and means for continuing the alteration of the potential on said switching grid electrode at least until the alteration of the potential of all the target electrodes is terminated.

8. Apparatus for pre-setting at a predetermined beam position the electron beam of a magnetron type multiple position beam switching tube having a cathode and a plurality of arrays of individual electrodes, an electrode from each array being associated together to define a beam position, said apparatus comprising means for altering the potential of all the electrodes of one array to induce the electron beam in the tube to advance from beam position to beam position in a self controlled stepby-step manner, means for altering the potential on an electrode associated with a predetermined beam position to inhibit the further advancement of said electron beam beyond said predetermined beam position, means for continuing the alteration of the potential on said electrode associated with a predetermined beam position until the alteration of the potential of all the electrodes of said array of electrodes is terminated.

9. In a magnetron type multiple position beam switching tube having a cathode and a plurality of arrays of individual electrodes, an electrode of each array being associated together to define a beam position for the electron beam formed between said cathode and said arrays of electrodes, apparatus for pre-setting said electron beam at a predetermined beam position comprising means for altering the potential difference between the cathode and the electrodes of at least one of said arrays to induce the electron beam in the tube to advance from beam position to beam position in a self controlled step-by-step manner, means for altering the potential on an electrode associated with a predetermined beam position to inhibit the further advancement of said electron beam beyond said predetermined beam position, and means for continuing the alteration of the potential on the last mentioned electrode at least until the alteration of the potential of all the electrodes of said array of electrodes is terminated.

10. In a magnetron type multiple position beam switching tube having a cathode and a plurality of arrays of individual electrodes including a spade array, a target array and a switching grid array, an electrode of each array being associated together to define a beam position for the electron beam formed between said cathode and said arrays of electrodes, apparatus for pre-setting said electron beam at a predetermined beam position comprising means for altering the potential of the switching grid array to induce the electron beam in the tube to advance from beam position to beam position in a self controlled step-by-step manner, means for altering the potential on a different electrode associated with a predetermined beam position to inhibit the further advancement of said electron beam beyond said predetermined beam position, and means for continuing the alteration of the potential on the last mentioned electrode at least until the alteration of the potential of all the electrodes of said array of electrodes is terminated.

ll. in a magnetron type multiple position beam switching tube having a. cathode and a plurality of arrays of individual electrodes, an electrode of each array being associated together to define a beam position for the electron beam formed between said cathode and said arrays of electrodes, apparatus for pre-setting said electron beam at a predetermined beam position comprising means for altering the cathode potential to induce the electron beam in the tube to advance from beam position to beam position in a self controlled step-by-step manner, means for altering the potential on an electrode associated with a predetermined beam position to inhibit the further advancement of said electron beam beyond said predetermined beam position, and means for continuing the alteration of the potential on the last mentioned electrode at 12 least until the alteration of the cathode potential is terminated.

12. In a magnetron type multiple position beam switching tube having a cathode and a plurality of arrays of individual electrodes, an electrode of each array being associated together to define a beam position for the electron beam formed between said cathode and said arrays of electrodes, apparatus for pre-setting said electron beam at a predetermined beam position comprising means for altering the potential of all the electrodes of at least one of said arrays to induce the electron beam in the tube to advance from beam position to beam position in a self controlled step-by-step manner, means for altering the potential on an electrode associated with a predetermined beam position to inhibit the further advancement of said electron beam beyond said predetermined beam position, and means for continuing the alteration of the potential on the last mentioned electrode at least until the alteration of the potential of all the electrodes of said array of electrodes is terminated.

13. Beam switching and indexing apparatus comprising a magnetron type multiple position beam switching tube having a cathode and a plurality of arrays of individual electrodes including a spade array, 21 target array and a switching grid array, an electrode of each array being associated together to define a beam position, a source of positive potential, means conductively connecting each of said spades and each of said targets to said source of positive potential, a source of bias potential, means including a separate impedance element associated with each switching grid for conductively connecting said switching grids to said source of bias potential, an electron tube having at least a cathode, a grid and an anode,

said electron tube being conductively connected between the cathode of said beam switching tube and a source of reference potential, means for applying an additional biasing potential to at least one of said switching grids, and means including a substantially unidirectionally conductive member for applying said additional bias potential to an electrode of said electron tube to control the electron flow through said electron tube.

14. Beam switching and indexing apparatus comprising a magnetron type multiple position beam switching tube having a cathode and a plurality of arrays of individual electrodes including a spade array, a target array, and

a switching grid array, an electrode of each of said arrays being associated together to define a beam position, a source of potential which is positive with respect to the cathode, each of the spade electrodes and each of the target electrodes being conductively connected thereto, a bias potential source, each of said switching grids being conductively connected to said bias potential source through a separate impedance element, means for applying an additional biasing potential between predetermined individual switching grids and the separate impedance element associated therewith, and means for advancing the electron beam from one beam position to another including a resistive element connected in series between said bias source and said separate impedance elements. 15. Beam switching and indexing apparatus comprising a magnetron type multiple position beam switching tube having a cathode and a plurality of arrays of individual electrodes including a spade array, a target array, and a switching grid array, an electrode of each of said arrays being associated together as a beam position, a source of potential which is positive with respect to the cathode, each of the spade electrodes and each of the target electrodes being conductively connected to said sources of potential which is positive with respect to the cathode, a biasing potential source, each of said switching grids being conductively connected to said bias potential source through a separate impedance element, means for applying a potential between predetermined individual switching grids and the separate impedance element associated therewith, and a plurality of means for advancing utilized in indexing the electron beam by lowering the po l tential of each target electrode except the one at the indexing beam position.

It is likewise practical to use the present invention to index the electron beam at a predetermined beam position when the tube is turned on initially. If the potentials applied to the tube are in the range to produce oscillation of the electron beam, transient effects may be utilized to cause the electron beam to be formed in the tube, and then indexing is accomplished by raising the potential of a switching grid, for example.

When it is desired to index the electron beam at a single beam position by means of altering the potentials of the targets, each of the targets except the target of the index position may be connected to its voltage source through a variable impedance such as an electron tube. Thus, when indexing the electron beam in the tube, a (negative) impulse to the control element (grid) of the tube would increase the tube impedance, cause a larger potential drop thereacross, and thereby lower the potential on the nine targets which are so connected.

Such an arrangement may be useful also as a supplemental beam indexing means other than the ones described before since it is of course not necessary to lower the potential of all switching electrodes and then raise again the potential of the switching electrode of the indexing position. Also the tube type variable impedance could be replaced by a high resistance connected in series with the supply potential of the nine switching electrodes. The high resistance would be shunted by a switch except when the beam is to be indexed. It can be seen that in this arrangement the target current is used to provide the required potential drop across the high resistance to lower the potential on these nine targets.

What is claimed is:

1. Apparatus for pre-setting at a predetermined beam position the electron beam of a magnetron type multiple position beam switching tube having a cathode and a plurality of arrays of individual electrodes, an electrode from each array being associated together to define a beam position, said apparatus comprising means for altering the potential between the cathode and the electrodes of at least one of said arrays to induce the electron beam in the tube to advance from beam position to beam position in a self controlled step-by-step manner and means for altering the potential on an electrode associated with a predetermined beam position While the first mentioned potential is altered to inhibit the further advancement of said electron beam beyond said pretermined beam position, and means for altering the second named potential on the electrode at least until the alteration of the first said potential of all the electrodes of said array of electrodes is terminated.

2. Apparatus for pre-setting at a predetermined beam position the electron beam of a magnetron type multiple position beam switching tube having a cathode and a plurality of arrays of individual electrodes, an electrode from each array being associated together to define a beam position, said apparatus comprising means for altering the potential of all the electrodes of one array to induce the electron beam in the tube to advance from beam position to beam position in a self controlled step-by-step manner, means for altering the potential on an electrode associated with a predetermined beam position to inhibit the further advancement of said electron beam beyond said predetermined beam position, and means for continuing the alteration of the potential on the electrode at least until the alteration of the potential of all the electrodes of said array of electrodes is terminated.

3. Apparatus for pre-setting at a predetermined beam position the electron beam of a magnetron type multiple position beam switching tube having a cathode and a plurality of arrays of individual electrodes, an electrode from each array being associated together to define a beam position, said apparatus comprising means for altering the cathode potential to induce the electron beam in the tube to'advance from beam position to beam position in a self controlled step-by-step manner, means for altering the potential on an electrode associated with a predetermined beam position to inhibit the further advancement of said electron beam beyond said predetermined beam position, and means for continuing the alteration of the potential on the electrode at least until the alteration of the potential of said cathode is terminated.

4. Apparatus for pre-setting at a predetermined beam position of the electron beam of a magnetron type multiple position beam switching tube having a cathode and a plurality of arrays of individual electrodes, including a spade array, a target array and a switching grid array, an electrode from each array being associated together to define a beam position, said apparatus comprising means for altering the potential of the electrodes of the switching grid array to induce the electron beam in the tube to advance from beam position to beam position in a self controlled step-by-step manner, means for altering the potential on an electrode associated with a predetermined beam position to inhibit the advancement of said electron beam beyond said predetermined beam position, and means for continuing the alteration of the potential on the electrode at least until the alteration of the potential of all the electrodes of said array of electrodes is terminated.

5. Apparatus for pre-setting at a predetermined beam position of the electron beam of a magnetron type multiple position beam switching tube having a cathode and a plurality of arrays of individual electrodes including a spade array, a target array and a switching grid array, an electrode from each array being associated together to define a beam position, said apparatus comprising means for altering the potential of the electrodes of the switching grid array to induce the electron beam in the tube to advance from beam position to beam position in a self controlled step-by-step manner, means for further altering the potential on a switching grid electrode associated with a predetermined beam position to inhibit the advancement of said electron beam beyond said predetermined beam position, and means for continuing the alteration of the potential on the electrode at least until the alteration of the potential of all the electrodes of said arroy of electrodes is terminated.

6. Apparatus for indexing the electron beam of a magnetron type multiple position beam switching tube at a predetermined beam position, said tube having a cathode and a plurality of arrays of individual electrodes including a spade array, a switching grid array and a target array, an electrode from each array being associated together to define a beam position, said apparatus comprising means for altering the potential of all the electrodes of one array to induce the electron beam in the tube to advance from beam position to beam position in a self controlled step-by-step manner, means for altering the potential of one of the electrodes associated with a predetermined beam position to inhibit the further advancement of said electron beam beyond said predetermined beam position, means for continuing the alteration of the potential on the said one electrode at least until the alteration of the potential of all the electrodes of said array of electrodes is terminated.

7. Apparatus for pre-setting at a predetermined beam position the electron beam of a magnetron type multiple position beam switching tube having a cathode and a plurality of arrays of individual electrodes, an electrode from each array being associated together to define a the electron beam, each of said means including a resistive element connected in series between said bias source and a plurality of said separate impedance elements, one of said plurality of means being adapted to advance the electron beam a number of beam positions which is controlled by the duration of the potential applied thereto, and the remainder of said plurality of means being adapted to advance the electron beam only a single beam position during the period any switching potential is applied thereto.

16. Beam switching and indexing apparatus comprising a magnetron type multiple position beam switching tube having a cathode and a plurality of arrays of individual electrodes including a spade array, a target array, and a switching grid array, an electrode of each of said arrays being associated together as a beam position, a source of potential which is positive with respect to the cathode, each of the spade electrodes and each of the target electrodes being conductively connected thereto, a bias potential source, each of said switching grids being con-- ductively connected to said bias potential source through a separate impedance element, means for applying an additional biasing potential between predetermined individual switching grids and the separate impedance element associated therewith, means for advancing the electron beam from one beam position to another including a resistive element connected in series between said bias source and said separate impedance elements, and further electron beam advancing means for altering the potential between said cathode and said spade array.

17. Beam switching and indexing apparatus comprising a magnetron type multiple position beam switching tube having a cathode and a plurality of arrays of individual electrodes including a spade array, a target array and a switching grid array, an electrode of each array being associated together to define a beam position, a source of positive potential, means conductively connecting each of said spades and each of said targets to said source of positive potential, a source of bias potential, means including a separate impedance element associated with each switching grid for conductively connecting said switching grids to said source of bias potential, an electron tube having at least a cathode, a grid and an anode, said electron tube being conductively connected between the cathode of said beam switching tube and a source of reference potential, means for applying an additional biasing potential to any of said switching grids, and means including a diode for applying said additional bias potential to an electrode of said electron tube to control the electron flow therethrough.

18. Apparatus for pre-setting at a predetermined beam position the electron beam of a magnetron type multiple position beam switching tube having a cathode and a plurality of arrays of individual electrodes, an electrode from each array being associated together, said apparatus comprising means for altering the potential level on an electrode of each beam position except the desired indexing position to change the beam holding characteristics at those beam positions where the electrode potential is altered and means for holding the potential at the altered level long enough for the said electron beam to advance in a self controlled manner until the index position is reached.

19. Apparatus for establishing at an indexing position the electron beam of a multiple position magnetron type beam switching tube having a cathode and a plurality of arrays of individual electrodes, an electrode of each array being associated together to define a beam position and wherein each electrode is coupled to a source of operating potential, comprising in combination, means for locking the beam into a stable condition at each position, a first circuit coupled between said cathode and one of said arrays to change the operating potential coupled to said array thereby causing the beam to be dislodged from a stable locked-in position, and a second circuit coupled to a single electrode in the array at the indexing position to retain that electrode at a potential such that the beam is stably locked in at the indexing position.

20. Apparaus as defined in claim 19 wherein the positions each include at least a spade and target electrode, and said first circuit is coupled to the cathode and the array of spade electrodes to reduce the spade to cathode potential.

21. Apparatus as defined in claim 19 wherein the positions each include at least a spade and target electrode, a high resistance is coupled in series with at least one target, and a switch is shunted to said high resistance to selectively cause the beam to be dislodged from the target when beam current impinges thereupon.

22. Apparatus for causing the electron beam of a multiple position magnetron beam switching tube with a cathode and a plurality of targets each having a corresponding beam forming and holding spade electrode to skip normally stable locked-in target positions comprising in combination, means for normally maintaining the targets, spades and cathode electrodes at an operating potential permitting the beam to advance from one successive target position to another, means for advancing the beam from one stable position to the next, means for establishing the potential of at least one of the electrodes at such polarity and of such magnitude that the beam will immediately advance automatically over the next successive target position, and means for establishing the potential of at least one other electrode subsequently presented to said beam at such polarity and magnitude that the beam will be locked into an indexed position.

23. A magnetron beam switching tube system comprising in combination, a cathode, a plurality of spaced beam forming and locking U-shaped electrodes arranged about said cathode with the apex directed toward the cathode, a plurality of target electrodes arranged about said spade electrodes and positioned to receive an electron beam in the form of a cathode current flowing between two adjacent spade electrodes, switching and auxiliary electrodes positioned respectively between each target and the corresponding two adjacent spade electrodes, means for causing the beam to be locked-in a stable position by beam current flowing to any of the spade electrodes, a circuit coupled to the auxiliary electrodes to produce an unstable beam condition and cause the beam to be dislodged from its locked-in position, and a circuit coupled to at least one of the switching electrodes to re-establish a stable locked-in position of the beam at a diiferent beam position.

References Cited in the file of this patent UNITED STATES PATENTS 2,591,997 Backmark Apr. 8, 1952 2,599,949 Skellett June 10, 1952 2,620,454 Skellett Dec. 2, 1952 

